Electronic circuit



Aug. 2, 1949. c FROMMER 2,477,976

ELECTRONIC C IRCUIT Filed Sept. 23, 1946 AAAAA AAAAAA new" IN V EN TOR.

C JosEpH G. EEOMMEE BYfimudoC & damn-mud ATT'OBNEYJ Patented Aug. 2, 1949 UNITED STATES PATENT OFFICE ELECTRONIC CIRCUIT Danville, Ill.

Application September 23, 1946, Serial No. 698,821

4 Claims. 1

This invention relates to an improved method and apparatus for controlling at all times the flow of current through a gas-filled tube having a control grid and a screen grid by simultaneously controlling the voltage on the screen grid and the control grid.

In many operations, particularly those involving photoelectric inspection operations of all kinds, although this invention is not limited to photoelectric inspection operations, it is desired to control the flow of current through a gasfilled tube by the independent and joint control of both the screen grid and the control grid in a gas-filled tube. It is impossible to prevent the flow of current through a gas-filled tube having both a screen grid and a control grid if the potential on the control grid exceeded a certain positive value of potential no matter how far the potential on the screen grid was driven in a negative direction. If the positive potential on the control grid does not exceed a certain value depending upon the operating characteristic of the tube and if the screen grid receives a sufficient negative potential, the screen grid will prevent starting of the flow of current through the tube. However, if the positive potential on the control grid exceeds a certain value, say, about a positive 13 volts, the tube will ionize in spite of any amount of negative potential which is placed on the screen grid, and, therefore, the screen grid has lost control of the tube insofar as preventing the tube from ionizing. This is only true of gas-filled tubes and is not true of vacuum tubes. However, gas-filled tubes have advantages over vacuum tubes and it is frequently desired to use them.

By my invention I make it possible for the screen grid to prevent ionization of the tube at any time if a sufficient negative potential is placed thereon and this is done by by-passing the excess voltage, which might be placed on the control grid, and cause the tube to ionize in spite of the negative voltage on the screen grid, which bypassing is so controlled to permit the tube to ionize if a sufficient positive potential is simultaneously placed on the screen grid.

Throughout the specification and claims whenever I speak of a positive or negative potential or a positive or negative bias, I means the relative potential or bias of the control grid with respect to its cathode. The cathode and grid may both be at a positive potential, but if the grid is more positive than the cathode, a positive bias or potential is placed on the grid. Likewise, both may have a positive potential, but if the grid is 2 less positive than the cathode, a relatively negative potential is placed on the grid.

Broadly my invention comprises a gas-filled tube having an anode circuit, a cathode circuit, a screen grid and a control grid. The control grid is connected to cathode potential through the rectifier which limits the maximum positive potential that can be placed on the control grid and yet permits a sufiicient potential to be placed on the control grid so that if the screen grid simultaneously receives a suitable potential, the gas-filled tube will ionize and conduct a current. However, if the screen grid is sufiiciently negative, the control grid by being subjected to a limited positive potential will not cause the gasfllled tube to ionize and conduct a current.

Any type of rectifier may be used. The rectifier must be arranged such that only a positive charge will pass through it from the control grid, i. e., with its anode toward the control grid. An ordinary vacuum tube rectifier may be used. Also a copper-oxide rectifier may be used. The cathode of the rectifier may be connected to the cathode of the gas-filled tube or to a resistor which, if a current flows across it, will cause a certain voltage difference between the cathode of the gas-filled tube and the cathode of the rectifier. The cathode of the rectifier may be connected to a resistor which passes current and then the value of the resistor determines the point at which the rectifier will by-pass all excess positive potential from the grid to the cathode circuit. Until that point is reached the rectifier passes nothing. Thus the rectifier controls the maximum positive potential that can be placed on the control grid.

Other advantages, uses and objects of my invention will become apparent by referring to the drawings in which Figure 1 illustrates an ordinary rectifying tube for accomplishing the by passing of the excess positive voltage from the control grid to the cathode circuit. Figure 2 shows a by-passing means comprising an ordinary vacuum tube having a control grid in which the anode is directly connected to the control grid.

In both Figures 1 and 2 specific means photoelectrically controlled are shown for applying the control voltages to the screen grid and control grid although it is understood that other means may be used and that the means illustrated are given only to demonstrate how the by-passing means functions.

Referring to the drawings, a gas-filled amplitying tube In is provided having an anode circuit II, a cathode circuit l2, a control grid I3 and a screen grid Id, The tube In is connected to a source of direct current potential having its positive potential at I and grounded at I6. In the particular illustration, a relay coil I! is provided in the anode circuit II which actuates the relay switch I8. In both Figures 1 and 2 the relay switch I8 is shown in the open position which is the condition when the tube I4 is non-ionized or non-conducting.

In both Figures 1 and 2 the devices are described in connection with a photoelectric inspection operation used, for example, for determining the size of an article. It may also be used for photoelectric registration control and the like. In order to close the relay switch I8 in Figures 1 and 2 it is necessary that the phototube I9 be in dark and the phototube 25] in light. It is understood that any other mean-s for placing a suitable potential with respect to the cathode I2 on the screen grid M and the control grid l3 which causes current to flow through the plate circuit II, actuating the switch I8, may be used. The circuits embodying the phototubes i9 and are merely illustrative of one way of doing this. The phototube It is connected to a source of direct current having its negative potential at 22 with the ground at 2|. The resistor is in series with the phototube i9 and the screen grid I4 is connected at point 24. When the phototube I9 is in darkness no current flows across resistor 29 and the screen grid Hi is on ground potential, and when the phototube I9 is in light, the screen grid l4 become-s negative due to photoelectric current flowing across resistor 29. When the phototube I9 is in light, the tube I0 cannot conduct a current even though the phototube 20 might conduct any amount of current when using my invention. In like manner the phototube 28 is connected in series with the resistor 25 and is also connected to a negative source of direct current potential at 2'? and the circuit comprising the phototube 28 and the resistor 25 is connected to B-\- at 25. The control grid I3 is connected between the phototube 29 and the resistor 25 at point 28.

Referring particularly to Figure 1, the control grid I3 is connected from point 29 to. the ground I6 through a rectifying tube 3!! and the part of an adjustable resistor 15! connected between ground and 3+. The vacuum tube has anode circuit 38 and a cathode circuit 32.

With the tetrode type of gaseous tube It]. any potential above around minus two volts on the control grid 13 will cause the tube IE! to ionize providing the screen grid M'is not below a negative voltage depending on the tube type. However, if the positive potential on the control grid I3 with respect to its cathode circuit I2 increases above about +13 volts, the tube ill will ionize even though a minus potential as high as several hundred volts should be placed on the screen grid I4. However, by using the tube 3% a by-pass is provided and the amount of potential received by the control grid is limited to a predetermined maximum value. By adjusting the adjustable resistor SI any voltage placed. at point 29 due to tube 2% being in light above a certain value can be by-passed to the ground l6. For example, the resistor 3! can be set so that any positive voltage placed on point 29 in excess of five volts is-by-passed to the ground I6 which prevents the control grid l3 from receiving at any time a positive voltage in excessof five volts and yet a positive five volts on the grid I3 is sufficient'for the tube It) to conduct if a suiiicient voltage is placed on the screen grid I4. Therefore, the control grid I3, when tube 20 is in light, receives suificient voltage to cause tube III to ionize provided a suitable voltage is placed on the screen grid I4, but yet if the screen grid I4 should be sufficiently negative, the tube will not ionize. This has been heretofore impossible when an excessive positive voltage was placed on the control grid I3. By means of adjustable resistor 3|, the point at which tube 30 will conduct and by-pass the excess voltage over a certain amount can be adju'sted. Thus, I have provided a means for insuring at all times the control of the flow of current through the tube It! independent of the positive voltage initiated by an outside source of direct potential such as the source supplied at the point 26. It eliminates the adjustment of illumination of the phototube and permits the joint control of the flow of current through the tube 10 by the control grid I3 and the screen grid I4. Such joint control is often desired in inspection operations of all kinds.

it is understood that while I have illustrated the screen grid IE and the control grid I3 being controlled by photoelectric means, that any means for controlling the two grids may be used depending upon the type of control desired. My invention resides in the by-passing of excess volt: age which may be applied to the control grid I3 in order that if the screen grid I4 is negative, the gas-filled tube ID will not conduct a current. It has not been found satisfactory to have such control directly tied up with the means for controlling the control grid. Suflicient current must flow from the point 26 in order to insure that the tube I0 Will conduct when the screen grid I' l also receives a positive potential. It would be difiicult to obtain an exact balance by having some sort of control tied up with the control means for the control grid. Therefore, my invention has considerable advantage over the devices of the prior art.

Figure 2 diiTers from Figure 1 in that a different type of rectifying tube is used. Any vacuum tube which'in essence has only a cathodecircuit and an anode circuit may be used. In FigureZ a vacuum tube 33 is provided having an anode 3d, a cathode 35 and a control grid 36. The anode 34 is connected directly with the grid at the point 37 so that in efiect the flow of current is from the grid 35 to the cathode 35 or it could be used for any desired control action. In a similar manner although it is not deemed necessary to illustrate it, the anode 34 could be connected directly to the cathode 35. The amount of voltage received by the point 29 which Will'be bypassed by the tube 33 to the ground I6 depends upon the amount of adjustment of the adjustable resistor 3I in the same manner as is done in Figure 1. b

The relay switch I8 is given as illustrativeof the type of control which may be used. The relay switch I8 may actuate a motor or an accept and reject mechanism where articles are sorted for size. It is also within the scope of my invention that instead of the relay coil H, a neon lamp or other indicating means may be embodied in the anode circuit II for indicating the results of the operation.

I-cl'aim as my invention: U

1. An electronic circuit comprising a gas-filled amplifying tube having an anode circuit, a cathode circuit, a screen grid and a control grid, said screen grid and said control grid jointly controh ling the flow of current through the amplifying tube, voltage applying means for controlling the bias on the screen grid, independent voltage applying means controlling the bias on the control grid and means for preventing a positive voltage from being placed on the control grid from said independent voltage applying means above a certain predetermined maximum value comprisin a rectifier type vacuum tube and a resistor connected in series from said control grid to said cathode circuit, said maximum value being such as to cause ionization of the gas-filled tube when a positive bias is placed on the screen grid and such that it would not cause said gas-filled tube to ionize when a negative bias is simultaneously placed on the screen grid.

2. An electronic circuit comprising a source of power, a gas-filled amplifying tube connected to said source, said tube having an anode circuit, a cathode circuit, a screen grid and a control grid, said screen grid and said control grid jointly controlling the flow of current through said amplifying tube, voltage applying means for controlling the voltage on the screen grid, independent voltage applying means for controlling the voltage on the control grid, and a series circuit comprisin a rectifier and a resistor connected from said control grid to said cathode circuit whereby only a positive potential will be passed by said rectifier from said control grid to said cathode circuit.

3. An electronic circuit comprisin a gas-filled amplifying tube having an anode circuit, a cathode circuit, a screen grid and a control grid, said screen grid and said control grid jointly controlling the flow of current through the amplifying tube, voltage applying means controlling the bias on the screen grid, independent means for controlling the bias on the control grid, voltage applying means preventing a positive bias from being placed on said control grid from said independent voltage applying means above a certain predetermined maximum value by said independent means comprising a rectifying tube and a resistor connected in series from said control grid to said cathode circuit, said rectifying tube having its anode connected to the control grid and its cathode connected to the said cathode circuit of said gas-filled tube thereby permitting only a positive potential to pass from said control grid to said cathode circuit, said maximum value being fixed by said resistor such as to cause ionization of the gas-filled tube when a sufficient positive bias is placed on the screen grid and such that it does not cause said gas filled tube to ionize when a sufficient negative bias is simultaneously placed on the screen grid.

4. An electronic circuit comprising a source of power, a gas-filled amplifying tube connected to said source, said tube having an anode circuit, a cathode circuit, a screen grid and a control grid, said screen grid and said control grid jointly controlling the flow of current through said amplifying tube, voltage applying means controlling the voltage on the screen grid, independent voltage applying means controlling the voltage on the control grid, a rectifier connected from said control grid to said cathode circuit whereby only a positive potential will be passed by said rectifier from said control grid to said cathode circuit.

JOSEPH C. FROMMER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,237,661 Ernst Apr. 8, 1941 2,315,926 Bivens Apr. 6, 1943 2,408,764 Edgerton Oct. 8, 1946 

